The present invention relates to the provision of a coupling allowing transmission of light between a polymer waveguide (PWG) array and a silicon waveguide (SiWG) array. More specifically, the present invention relates to a technique for providing high-precision alignment of arrays in a single-mode polymer waveguide (PWG) so that an adiabatic coupling is provided.
Both multi-mode and single-mode polymer waveguides (PWG) are widely used in either a rigid form on a printed board or in a flexible form on a polymer base film.
The principle of an optical waveguide (WG) is that a combination of core and clad is provided and the core is used as a light transmitting path. The combination of core and clad is a combination of two different types of polymers having a different refractive indexes.
Silicon waveguides (SiWG), in which a light transmitting path is fabricated on a silicon (Si) chip, are also widely used.
In both the polymer waveguide (PWG) and in the silicon waveguide (SiWG), multi-channel waveguides (WG) are fabricated in array in one direction in parallel with each other so that multi-channel light transmitting paths are provided. Attempts have been made to transmit light between the polymer waveguide (PWG) and the silicon waveguide (SiWG). However, a coupling which allows light to be transmitted efficiently at the microscopic level requires high-precision positioning.
In the case of multi-mode waveguides (WG), when the waveguides are coupled to each other or when the waveguide is coupled to a multi-mode optical fiber, a large cross section of core, almost the same size of core cross section, and almost the same numerical apertures can provide such coupling with an acceptable level of loss as long as a precise positioning of the abutting cross sections is guaranteed between the cross sections coming into connection with each other. Actually, what is called a “Butt Coupling” is used to provide the above coupling.
However, when a single-mode waveguide (WG) is coupled to a silicon waveguide (SiWG), the cross section of core is very small and the connected waveguides are very different from each other in the size of core cross section and in the numerical aperture. Thus, it is very difficult to use the Butt Coupling. In this case, adiabatic coupling can be used as an alternative method by which evanescent light in an optical axis direction along the array is captured and transmitted over a predetermined distance in the optical axis direction.
However, a technique is still unknown which, when a single-mode waveguide (WG) is coupled to a silicon waveguide (SiWG), provides high-precision alignment of arrays to provide the adiabatic coupling.
Concerning innovative methods for fabricating polymer waveguides (PWG) or positioning multi-channel polymer waveguides (PWG), a variety of elemental techniques are known. However, there is no known literature which provides the adiabatic coupling or refers to high-precision alignment, such as self-alignment for providing the adiabatic coupling.